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﻿OVERALL DIFFICULTY INDEX: 3/10

IF YOU HAVE NO TOOLS YOU SPEND $ 40 TO GET THEM FOR THIS JOB

IF YOU HAVE NO EXPERIENCE YOU SPEND 2 HOURS TO CARRY OUT THIS JOB

RISK OF BURNS - SEE BELOW

BEFORE YOU START

Always work on cold engines except when the engine needs to be hot as explained below.

Make sure to keep your hands away of the exhaust and the turbo to avoid burns.

Note: The below works occurred on a Peugeot 5008 equipped with an PSA-BMW EP6 direct injection and turbocharged engine in its 156HP version. Works remain similar for other engines and identical for Citroen, Mini, Saab and Peugeot vehicles equipped with the same engine.

DISCLAIMER:Our pictorials are of informative nature and do illustrate works carried out by ourselves at our own premises for our own use and satisfaction. Readers who envisage to carry out similar works inspired by the below method shall do this at their own risks and liability.

How a turbo vacuum line works

The turbo is controlled by its waste gate valve.The latter uses a vacuum actuator (left) fed from a vacuum pump (middle left) via a solenoid valve (middle right), the turbo regulation valve.A vacuum tank serves as a buffer for ensuring a smooth control of the waste gate valve (not possible to have a good picture on this vehicle, it's the black box showing on the middle of the picture to the right)

Using a vacuum gauge for testing the turbo vacuum regulation

Vacuum is a pressure lower than the atmospheric pressure, called negative pressure.Specific vacuum gauges for car diagnostic exist but you can also use vacuum gauges for pneumatic systems as it is the case here.​It is graduated from 0 to -1 (full vacuum).You need to fit it with an accessory to which a rubber hose can be connected and that's it ​ (see further below in the pictorial).

How to troubleshoot the turbo vacuum regulation system

Start by purchasing a hose connector of the same diameter than the largest vacuum connector in your vehicle.This is usually the one connecting the servo brake vacuum hose to the vacuum pump (left).Unplug it (middle) and match your connector (right). An 8 mm rubber hose in this case. Any air or fuel hose will do.

The below shows the manufacturer's recommendations for the vacuum pump testing showing the maximum allowable time for the vacuum to reach a particular value. Engine should be hot for this test.

Step 1: test the brake vacuum outlet

Plug your vacuum gauge into the vacuum pump brake connector.You may prepare your watch to count the seconds but a good pump will usually reach almost full vacuum in a second.Ask someone to start the engine and observe the vacuum gauge.In this case, it reached -0.98 bars in less than a second denoting no trouble on the brake outlet side.

Step 2: test the turbo vacuum outlet

Start by removing all air hoses for an easier reach to the brake vacuum pump.The smaller vacuum hose of the turbo control circuit is visible in the middle of the right picture:

Change the vacuum gauge rubber hose to a smaller one (6 mm) and repeat the procedure while plugging the vacuum gauge into the turbo regulation vacuum outlet of the vacuum pump.

​In this case, the vacuum gauge needle kept oscillating for several seconds and never reached the full vacuum like on the brake outlet side.Upon turning off the engine, it started immediately moving towards zero.No doubt the check valve inside the turbo vacuum connector is damaged (see our "brake vacuum pump maintenance" page for details)

If your vacuum pump failed the above test, you may attempt to clean it or decide to replace it with a new one.Pour some engine oil of the same quality than the one you use for your engine on the new vacuum pump drive prior to assembling it.

To understand how this test works, plug your scanner into your vehicle and go to the page showing you the waste gate valve control OCR.You will notice it is close to the maximum (85%, almost closed, vacuum force needed) when engine is idling and goes down to 23% (almost open, no vacuum needed) as soon as you press on your gas pedal.